A filter press is an economic and efficient liquid/solid separation device commonly utilized in the clay, chemical, or mining industries. Filter presses generally employ a plurality of filter plates, each filter plate having large areas of a textile material to form a filtering screen. The textile material is typically attached to a cloth, rubber or plastic tubular hub. The tubular hub allows the material to be filtered to pass through successive filtering chambers in the press. The tubular hub must be securely attached to the filtering material to prevent leakage, and is usually constructed of a textile tube or a thermoplastic or rubber material.
In the current state of the art, filter cloth is generally installed on the filter plates by rolling up one side of a duplex filter cloth, which is joined at a feed hole with the tubular hub, and then pushing the rolled up filter cloth through the feed hole of the filter plate. After passing the rolled cloth through the feed hole, the filter cloth is then unrolled. The filter plate thus has a layer of filter cloth on either side thereof, and the two filter cloth layers are fastened together on the filter plate. Slurry is pumped into the filter press and fills each cavity within the stack of filter plates. Solids remain in the chambers and filtrate passes through the cloth, exiting the filter plate.
Conventional methods for joining the filtering material to the tubular hub include sewing the two filter cloth layers together. This approach is labor intensive and thus expensive. Moreover, the sewing tends to create weaknesses in the joint due to the stitch holes. Stitching can also be difficult due to the thickness of the filter cloth and the tubular hub. Other methods include adhesive and bonding agents to secure the filtering cloth to the tubular hub, but these techniques are time consuming since the adhesive must set to form the bond, and is not consistently reliable. Welding requires a split clamping collar positioned between the flanges of the feed neck to transmit force to the weld from a clamping cylinder.
U.S. Pat. No. 4,765,859 describes a method of joining filter cloth to a rubber tubular hub for use as a filter screen, which is installed on a filtering plate in a filtering press. The hub consists of a cylindrical tube that includes two annular flanges protruding radially outward from the circumference of the tube at each end. The tubular hub is fabricated from a rubber material that is collapsible. A filtering screen is then constructed by joining two filter cloths to the hub at each end of the tube. One filter cloth is joined to the hub at the inside surface of one flange, while the other filter cloth is joined to the inside surface of the other flange. The filter cloth and hub are bonded together by induction heating to form a seal to prevent leakage of the filtered material.
U.S. Pat. No. 5,958,173, the contents of which are herein incorporated by reference, describes a method of fabricating a filter screen for a filter press by attaching a filter cloth to a tubular hub using induction heating.
The methods in the prior art of attaching a filter cloth to a filter plate pose a number of disadvantages. The prior methods of installing filter cloths are difficult and time consuming, particularly for larger filters (up to 2 meters by 2 meters square). The large cloth requires a person on each side of the filter plate: one person to push the filter cloth through the hole, and the other person to receive the filter cloth. Large presses are usually re-clothed without removing plates, requiring operators to get between the plates physically, sometimes on platforms above conveyors or high above the ground level, a procedure that can be dangerous. The removal of filter plates in order to replace the filter cloths causes significant losses in productivity, as the filter press cannot be used during the replacement process.
Furthermore, the duplex-type of filter cloths used in the prior art can be expensive, as both layers of a duplex filter cloth must be removed and replaced when a hole forms in only one of the layers. The process of assembling the duplex filter cloths on a flanged tube for attachment to a filter plate is also complex and unwieldy.
It is thus desirable to find a new method for securely joining a filtering material such as a cloth fabric or synthetic material, as commonly used in filtering applications, to a filter plate.